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The KC-97 Stratofreighter was an aerial refueling tanker variant of the C-97 Stratofreighter (which was itself based on the Boeing B-29 Superfortress), greatly modified with all the necessary tanks, plumbing, and a flying boom. The cavernous upper deck was capable of accommodating oversize cargo accessed through a very large right-side door. In addition, transferrable jet fuel was contained in tanks on the lower deck (G-L models). Both decks were heated and pressurized for high altitude operations.

Note: Occasionally the KC-97 has been referred to as "Stratotanker". However, all reputable sources refer to the KC-97 as Stratofreighter, not -tanker. This includes both Boeing and the USAF themselves.[6][7]

The USAF began operating the KC-97 in 1950. It purchased a total of 811 KC-97s from Boeing,[5][8][9] as opposed to only 74 of the C-97 cargo version.[10][11][12] The KC-97 carried aviation gasoline for its own piston engines but it carried jet fuel for its refueling mission, this required an independent system for each type of fuel. However, it was able to offload its aviation gas to a receiver in an emergency in a procedure known as a "SAVE".[citation needed]

These tankers were vitally important to the world-wide Boeing B-47 Stratojet strategic operations. An example was the support of Arctic reconnaissance flights from Thule Air Base.

While it was an effective tanker, the KC-97's slow speed and low operational altitude complicated refueling operations with jet aircraft. B-52s typically lowered their flaps and rear landing gear to slow the aircraft enough to refuel from the KC-97. In addition, a typical B-52 refueling engagement profile would involve a descent that allowed the aircraft pair to maintain a higher airspeed (220–240 knots). In the early 1960s, the Tactical Air Command added General Electric J47 two twin- jet pods from retired KB-50 aerial tankers to produce the KC-97L. These jet pods increased the speed of the KC-97 (for short periods of time) and made it more compatible with jet fighter planes like the F-84, F-100, and F-101.

This modified KC-97, constructed in 1953, was eventually purchased by NASA in 1997. It is still in service supporting NASA, other Federal agencies, and Federal contractors. It is one of two KC-97s left still in flyable condition, the other being former KC-97G 52-2718, "Angel of Deliverance", currently flown by Berlin Airlift Historical Foundation as YC-97A 45-59595.

Three C-97As were converted into aerial refueling tankers with rear loading door removed and a flight refueling boom added. After the design was proven, they were converted back into the standard C-97A.

KC-97E

aerial refueling tankers with rear loading doors permanently closed, 60 built. Some were later converted into transports as the C-97E.

KC-97F

3800hp R-4360-59B engines and minor changes, 159 built. Some were later converted into transport as the C-97F.

29 October 1957 – KC-97G AF Ser. No. 52-2711 of the 509th Bomb Wing,[24] out of Walker AFB, New Mexico, crashed 35 miles north of Flagstaff, Arizona, while on a nine-hour low-level survey flight to determine minimum altitude restrictions for B-47 training routes. The aircraft was seen over Gray Mountain, Arizona, at altitude of 60 feet shortly after 0830 hrs., and then heard striking a cloud-shrouded cliff face, killing 16 crew and strewing wreckage for 200 yards along mountainside.[25][26]

14 December 1959 – KC-97G AF Ser. No. 53-0231 of the 384th Air Refueling Squadron, out of Westover AFB, Massachusetts, collided with a B-52 during a refueling mission at an altitude of ~15,000 feet. The aircraft lost the whole left horizontal stabilizer and elevator, the rudder, and the upper quarter of the vertical stabilizer. The crew made a no-flap, electrical power off landing at night at Dow AFB, Maine; seven crew okay. "Spokesmen at Dow Air Force, Bangor, said the B52 [sic] apparently 'crowded too close' and rammed a fuel boom into the tail of a four-engined KC95 [sic] tanker plane."[30] Aircraft stricken as beyond economical repair. Two crew on the B-52 ejected, parachuted safely, and were recovered by helicopters in a snow-covered wilderness area. The bomber and remaining eight crew safely landed at Westover AFB.[31]

30 March 1960 – KC-97 AF Ser. No. 51-0363 (Manufacturer's Serial Number 16430) ditched and sank off Cape Canaveral. This particular aircraft was lost due to engine failure. The crash resulted in 3 fatalities of the 14 crew. The wreck of the aircraft was discovered June 6, 2015, in 365 feet of water by divers.[32]

27 June 1960 – KC-97G AF Ser. No. 52-2728 of the 380th Air Refueling Squadron, Plattsburgh AFB, New York, suffered failure of lubrication on an engine impeller shaft during an evening four-hour training mission to refuel a Boeing B-47 Stratojet. During rendezvous at 15,500 feet, the tanker's number one (port outer) powerplant caught fire. As the bomber moved away from the burning tanker, the crew tried unsuccessfully to put out the blaze. The plane went into a spin as the wing failed outboard of the engine; the aircraft crashed on Jonathan Smith Mountain, a hill east of Puzzle Mountain in Newry, Maine. The flash of the fire was seen from as far away as Lewiston and Bridgton. All five crew were killed. Wreckage covering five acres was still there as of 2010.[35][36][37]

5 November 1964 – KC-97 AF Ser. No. unknown of Pease Air Force Base crashed on takeoff; all five crewmen were killed.[38][39][40]

17 September 1971 – KC-97G IAF Serial 4X-FPR/033 of the Israeli Air Force, was shot down by Egyptian missiles over Suez, Egypt; seven of eight-man crew were killed.[41]

A number of KC-97s survive, at least two of which are potentially airworthy: 52-2718 / N117GA Angel of Deliverance is currently airworthy and operated by the Berlin Airlift Historical Foundation.,[42] and N1365N known as Tanker 97 and operated until about 2004 as an aerial firefighting airtanker by Hawkins & Powers.